Re: MP-safe ifnet with psz & psref

[Thor Lancelot Simon <tls%panix.com@localhost>]

I do not think you should do any extra work to support kvm grovelling.

On Tue, May 10, 2016 at 12:07:12PM +0900, Ryota Ozaki wrote:
> On Thu, Apr 28, 2016 at 4:04 PM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> > Hi,
> >
> > This proposal is the first step toward making interfaces
> > (struct ifnet) MP-safe; it applies psz and psref to ifnet
> > and ifnet_list to safely look up ifnets from ifnet_list
> > and safely remove an ifnet.
> >
> > Here is a patch:
> >   http://www.netbsd.org/~ozaki-r/psref-ifnet.diff
> 
> I restored the original ifnet_list because the change broke
> netstat -i (kvm(3)). So we now maintain two ifnet lists while
> the original list is only added/removed elements and not
> referenced by say IFNET_FOREACH. It's redundant but its overhead
> is negligible and it's the easiest way to keep backward
> compatibility. Of course, ideally we should kill kvm(3) users
> and remove the original list, but it's not now, I think.
> 
> Objection?
> 
>   ozaki-r
> 
> >
> > One concern is m_reclaim that can be run in hardware
> > interrupt and so the patch skips if_drain if it's
> > running in hardware interrupt because pserialize is
> > basically designed used in lwp or softint (and now
> > psref is used with IPL_SOFTNET). Is there a better
> > solution?
> >
> > And any other suggestions and comments would be
> > appreciated.
> >
> > Thanks,
> >   ozaki-r
> >
> > P.S. From today for ten days, I'll be unable to use
> > my main development machines, I wouldn't be able to
> > update and test patches reflected your feedbacks enough.

-- 
  Thor Lancelot Simon	                                     tls%panix.com@localhost

  "We cannot usually in social life pursue a single value or a single moral
   aim, untroubled by the need to compromise with others."      - H.L.A. Hart